Field of the Invention
The present invention relates to a method of mounting an electronic part, a circuit substrate, and an image forming apparatus. In particular, the present invention relates to a method of mounting an image density detector including a light emitting element and a light receiving element.
Description of the Related Art
A color image forming apparatus is required to have precise color reproducibility and tint stability, and therefore some color image forming apparatus have an automatic image density control function. In particular, because the tint is changed due to a change of operating environment or use histories of various consumable items, it is necessary to regularly perform the image density control so as to always stabilize the tint. In order to perform this image density control, there is known a structure in which the image forming apparatus includes an optical image density detector for detecting a toner image (test toner patch) formed on an image bearing member such as an intermediate transfer belt. The image forming apparatus detects the test toner patch on the intermediate transfer belt by using the optical image density detector, and uses a toner adhesion amount calculated from a result of the detection for image adjustment.
In general, the optical image density detector has a detection structure in which light emitted from a light emitting element passes through a fine opening part (fine hole) having a diameter of approximately a few mm and irradiates the intermediate transfer belt or the toner patch on the intermediate transfer belt, and reflection light is detected by a light receiving element. The image forming apparatus calculates the toner adhesion amount on the intermediate transfer belt based on a light amount received by the light receiving element. In the image density detector, it is an important function affecting image adjustment performance to allow stable light to pass through the fine opening part having a diameter of approximately a few mm so as to detect a light amount variation of the toner patch with high accuracy.
The light emitting element and the light receiving element (hereinafter referred generically to as a light element) have an angle dependence of each of the light emission amount and light reception sensitivity. In addition, a positional displacement of the light element with respect to the opening part greatly affects a light emission amount and a light reception amount after passing through the opening part. Therefore, mounting position accuracy and inclination accuracy of the light element with respect to a position of the opening part are important. As measures for improving the mounting position accuracy of the light element, various related-art methods are proposed. For instance, there is known a mounting method involving using surface tension of molten solder to arrange light elements in a self-alignment manner (see, for example, Japanese Patent Application Laid-Open No. 2002-076602). In addition, there is known a mounting method involving disposing high stiffness indenters on an element to be mounted on the substrate, and integrally pressing the indenters with the use of a diaphragm to join the element and the substrate (see, for example, Japanese Patent Application Laid-Open No. H06-302945). By using those measures, it is possible to mount the light element on the substrate with little variation in mounting position of the light element.
However, in the related-art method of mounting the light element on the substrate in the image density detector, solder 1001 after a heating process has a spherical shape as illustrated in FIG. 7, and hence a light element 1002 is apt to be unstable on the spherical solder 1001 and to be inclined (in a double-headed arrow direction in FIG. 7). Therefore, a mounting angle of the light element 1002 on a circuit substrate 300 with respect to an opening part 312 may not be good, and hence performance of an image density detector 2000 may be deteriorated. Note that, FIG. 7 is a diagram of a cross section of the image density detector 2000 as viewed from the side face, and like reference numerals and symbols denote like structures to those in the embodiments described later so that description thereof is omitted.